If this is your first visit, be sure to
check out the FAQ by clicking the
link above. You may have to register
before you can post: click the register link above to proceed. To start viewing messages,
select the forum that you want to visit from the selection below.

The first question I have is, how big is this study compared to others, especially in terms of male and female participant ratios? And, are the ratios in this study representative of the ratios generally speaking of male to female divers on any given day? Do we even know what that approximate average ratio is?

The second question relates to male female differences in the circulatory system. Did I correctly understand from the study that women are slightly more disposed to DCS under the same conditions? And, can this be explained by differences between male and female circulatory systems and their relative rates of diffusion and perfusion?

Thirdly, the correlation of stress to increased DCS incidence is also very interesting. Might diving CCR lower stress if environmental stress factors are high, as opposed to OC? That would be my educated guess having survived a few high exertion very stressful dives where I definitely would've run out of gas and drowned if I had done those dives with an Al80.

The fourth question I have is, what exactly are the medium density tissues which factor more heavily into DCS incidents than the fastest and slowest tissues? This is perhaps the most perplexing idea, however small the incidence and sample size. The idea that the shortest and longest HT tissues are the least vulnerable to different pressure gradients within reasonsble conservatism settings is really confounding... -Andy

I am surprised by the lack of more interest measured by responses of this article. As rebreather divers and thus most of us doing decompression dives, has anybody wondered how GF's are supposed to be applicable to recreational divers?

The article states that increased GF's presuppose you to getting bent - based on data collected from recreational dives.

The first question I have is, how big is this study compared to others, especially in terms of male and female participant ratios? And, are the ratios in this study representative of the ratios generally speaking of male to female divers on any given day? Do we even know what that approximate average ratio is?

Good Question. I do not know the answer. I see more female recreational divers than female tech divers. I think IANTD tried to quantify this once.

The second question relates to male female differences in the circulatory system. Did I correctly understand from the study that women are slightly more disposed to DCS under the same conditions? And, can this be explained by differences between male and female circulatory systems and their relative rates of diffusion and perfusion?

I am not aware that there is a gender difference in circulation. The women in this study had a higher fat mass than the males. And there appeared to be a correlation of increased fat mass to predisposition to DCS as per this study. The causation of "undeserved" hits is one that is much more complicated than previously thought - an argument made in this article. From what I have read generally, it appears to be multifactorial. With regards to gender, there was no deliniation of fitness levels between the groups.

Thirdly, the correlation of stress to increased DCS incidence is also very interesting. Might diving CCR lower stress if environmental stress factors are high, as opposed to OC? That would be my educated guess having survived a few high exertion very stressful dives where I definitely would've run out of gas and drowned if I had done those dives with an Al80.

That goes to "other factors" that might increase susceptibility of getting bent. Hormonal factors....does increased heart rates increase gas uptake, increased work load increases gas uptake....our computers have no idea what we actually do and do not account for that. BUT: these where RECREATIONAL dives. If I am cold, worked harder than usual, etc, I add to my SHALLOW stops (and no, I am not restarting a deep stop debate). But for decompression divers using their knowledge, it would make sense to modify your deco plan according to the circumstances. Recreational divers have a very limited if any knowledge of decompression. Additionally, they are on a limited gas supply. I still wonder how "GF values" as "calculated" in recreational divers correlate to what we do. Please also note that the majority of divers bubbled but did not get bent. So when does the "bubble" (if that is really the causative agent) get us in trouble? Perhaps it is not "just" the bubble, but the bubble PLUS X. What X is and acts is exactly what a lot of researchers are trying to determine.

The fourth question I have is, what exactly are the medium density tissues which factor more heavily into DCS incidents than the fastest and slowest tissues? This is perhaps the most perplexing idea, however small the incidence and sample size. The idea that the shortest and longest HT tissues are the least vulnerable to different pressure gradients within reasonsble conservatism settings is really confounding... -Andy

"Tissues" are theoretical and not an actual body tissue such as brain, heart, muscle...What qualifies a tissue of being fast vs slow is a theoretical representation of gas uptake and release based on diffusion/perfusion and an assigned time factor. Why recreational divers would have a "slow" leading tissue group, is unclear to me.

"I am not aware that there is a gender difference in circulation. The women in this study had a higher fat mass than the males. And there appeared to be a correlation of increased fat mass to predisposition to DCS as per this study. The causation of "undeserved" hits is one that is much more complicated than previously thought - an argument made in this article. From what I have read generally, it appears to be multifactorial. With regards to gender, there was no deliniation of fitness levels between the groups."

-As I understand it, there definitely are dimorphic differences in circulatory function between men and women. Whether that manifests in gas exchange in blood and tissue is certainly beyond my expertise, hence my question. After a quick search of sex differences in the circulatory function, I found this:

-The article has lots of parts I do not understand, but the author posits that while male and female circulatory parts are identical and both are able to maintain homeostasis, they maintain it through different balances of physiologic components. And as divers and CCR divers particularly, we are all subjecting ourselves to stresses that our physiology is not adapted to. So, if there are sex differences in how our bodies regulate and maintain homeostasis, it stands to reason that those differences may result in different DCS risk.

Thirdly, the correlation of stress to increased DCS incidence is also very interesting. Might diving CCR lower stress if environmental stress factors are high, as opposed to OC? That would be my educated guess having survived a few high exertion very stressful dives where I definitely would've run out of gas and drowned if I had done those dives with an Al80.

"That goes to "other factors" that might increase susceptibility of getting bent. Hormonal factors....does increased heart rates increase gas uptake, increased work load increases gas uptake....our computers have no idea what we actually do and do not account for that. BUT: these where RECREATIONAL dives. If I am cold, worked harder than usual, etc, I add to my SHALLOW stops (and no, I am not restarting a deep stop debate). But for decompression divers using their knowledge, it would make sense to modify your deco plan according to the circumstances. Recreational divers have a very limited if any knowledge of decompression. Additionally, they are on a limited gas supply. I still wonder how "GF values" as "calculated" in recreational divers correlate to what we do. Please also note that the majority of divers bubbled but did not get bent. So when does the "bubble" (if that is really the causative agent) get us in trouble? Perhaps it is not "just" the bubble, but the bubble PLUS X. What X is and acts is exactly what a lot of researchers are trying to determine."

-All your points are well taken, agreed.

-The bubbling without DCS is very odd, as obviously one must have bubble formation to create a restriction of blood flow and tissue damage. Why are some bubbles apparently harmless and others not? Maybe it has something to do with the surfactant quality? Maybe some bubbles are more slippery than others and some more sticky and prone to lump together?

The fourth question I have is, what exactly are the medium density tissues which factor more heavily into DCS incidents than the fastest and slowest tissues? This is perhaps the most perplexing idea, however small the incidence and sample size. The idea that the shortest and longest HT tissues are the least vulnerable to different pressure gradients within reasonsble conservatism settings is really confounding... -Andy

" "Tissues" are theoretical and not an actual body tissue such as brain, heart, muscle...What qualifies a tissue of being fast vs slow is a theoretical representation of gas uptake and release based on diffusion/perfusion and an assigned time factor. Why recreational divers would have a "slow" leading tissue group, is unclear to me."

-I missed that, thanks. How can recreational divers saturate enough to have a slow leading tissue, and how did they measure this?

The fourth question I have is, what exactly are the medium density tissues which factor more heavily into DCS incidents than the fastest and slowest tissues? This is perhaps the most perplexing idea, however small the incidence and sample size. The idea that the shortest and longest HT tissues are the least vulnerable to different pressure gradients within reasonsble conservatism settings is really confounding... -Andy

" "Tissues" are theoretical and not an actual body tissue such as brain, heart, muscle...What qualifies a tissue of being fast vs slow is a theoretical representation of gas uptake and release based on diffusion/perfusion and an assigned time factor. Why recreational divers would have a "slow" leading tissue group, is unclear to me."

-I missed that, thanks. How can recreational divers saturate enough to have a slow leading tissue, and how did they measure this?

The medium tissues were the same ones that appeared (based on the HEAT maps) to have peak surfacing loads and presumably bend divers in NEDU's deep stop study...

Recreational divers might do 4 or more dives a day, those add up on "slow tissue" loads so that after surfacing at the end of a day, with air or perhaps 32% safety stops, the medium and slower tissues are going to be leading. It seems the GFs were developed/modeled from the profiles afterwards, not measured with physical data.

Thank you Silent Running for finding this article "Sex and the cardiovascular system: the intriguing tale of how women and men regulate cardiovascular function differently"

Some thoughts:

"Under conditions of cardiovascular stress (e.g., exercise, loud noises, or psychological stress) men respond by increasing mainly vascular resistance (TPR in*Eqs. 2*and*3), which is manifested as an increase in mean Pa*(blood pressure) (2), whereas women predominantly increase HR (Eq. 1), thereby increasing CO. In both cases, there is an appropriate cardiovascular response, but there are potentially different outcomes."

An increase in vascular resistance suggests a decrease in gas uptake, whereas an increase in HR might increase gas uptake

"Recall further that the control of blood pressure involves actions of the autonomic nervous system. On the one hand, there is a sympathetic drive (by analogy, the accelerator) to the heart and periphery. Increases in sympathetic activity in the heart results in both elevated contractility, which leads to increases in SV, and increases in HR. Either or both actions lead to an increase in CO. In the periphery, increases in sympathetic activity results in resistance vessel constriction with an increase in TPR. Reduction or withdrawal of sympathetic activity is analogous to taking one's foot off of the accelerator, thereby reducing SV, HR, and TPR. On the other hand, the parasympathetic (vagal) system (by analogy, the brake) slows the heart; withdrawal of parasympathetic activity unmasks the sympathetic drive.

Recent studies of blood pressure control and cardiac function in healthy men and women have demonstrated that women and men use the two arms of the baroreflex system differently. At all ages, women were found to have reduced sympathetic activity (reflected by lower TPR and Pa) and enhanced parasympathetic activity relative to men".

An increase in parasympathetic activity would suggest a reduction in gas uptake but also a decrease in off-gassing. Increased sympathetic activity with increased cardiac output suggests an increase in gas uptake but coupled with peripheral vascular constriction, decreasing gas uptake. Net effect? An net increase in cardiac output could aid in off-gassing.

This pertained to "healthy" males and females. People who have altered cardiovascular system due to hypertension/coronary disease/diabetes etc, have altered perfusion characteristics. It appears by this article that there exists a genetic difference between male and female compensatory mechanisms.

Looking over the DAN Europe study, in the DCS group, I noticed that the age distribution of females between 10 years of age to 82. The male age distribution was between 23 - 67 years of age, although the mean was 37/42.

The DAN Europe study also points out that although females had a higher propensity of getting bent notwithstanding similar bubble formation compared to males. Suggesting (indirectly) that gas uptake and off-gassing characteristics where similar?

While looking for "triggers" of DCS, it appears that studies of this phenomena need to differentiate their approach to allow for gender differences.